216 - Slice

[lvjiaxuan]

It's so extreme level as so much time I had spent to solute it.

Playground.

// #4425
type _GreaterThan<T extends number, U extends number, Arr extends 0[] = []> =
  U extends Arr['length']
    ? T extends Arr['length']
      ? false // 相等
      : true // T 数字更大
    : T extends Arr['length']
      ? false // 先到达 T，证明 U 数字更大
      : _GreaterThan<T, U, [ ...Arr, 0 ]> // 两个都没到达

type _ToPositiveIdx<N extends number, Arr extends unknown[], _Counter extends 0[] = []> =
  `${ N }` extends `-${ infer I extends number }`
    ? _Counter['length'] extends I
      ? Arr['length']
      : Arr extends [ unknown, ...infer Rest ]
        ? _ToPositiveIdx<N, Rest, [ ..._Counter, 0 ]>
        : never
    : N

type _VerifyIdx<A extends number, B extends number, Max extends number> =
  _GreaterThan<A, B> extends true
    ? false
    : _GreaterThan<A, Max> extends true
      ? false
      : _GreaterThan<B, Max> extends true
        ? false
        : true


type Slice<
  Arr extends unknown[],
  Start extends number = 0,
  End extends number = Arr['length'],
  _Idx extends 0[] = [],
  _OverStart extends boolean = false,
  _Result extends unknown[] = [],
  _Start extends number = _ToPositiveIdx<Start, Arr>,
  _End extends number = _ToPositiveIdx<End, Arr>,
  _CurrentValue extends Arr[number] = Arr[_Idx['length']],
  _ValidIdx extends boolean = _VerifyIdx<_Start, _End, Arr['length']>,
> = _ValidIdx extends false
  ? []
  : _Idx['length'] extends _Start
    ? _Idx['length'] extends _End
      ? []
      : Slice<Arr, _Start, _End, [ ..._Idx, 0 ], true, [ _CurrentValue ]>
    : _OverStart extends false
      ? Slice<Arr, _Start, _End, [ ..._Idx, 0 ], false>
      : _Idx['length'] extends _End
        ? _Result
        : Slice<Arr, _Start, _End, [ ..._Idx, 0 ], true, [ ..._Result, _CurrentValue ]>